Vehicle handling and stability have been important areas of research for quite some time due to an increased focus on traffic safety and because of customer demand. Two common types of undesirable conditions that a vehicle, such as a car, may encounter are referred to as oversteering and understeering. Oversteering is the situation where the rear end of the vehicle moves towards the outside of a turn instead of following the curvature of the turn. Understeering is the opposite situation where the front end of the vehicle moves towards the outside of the turn instead of following the curvature of the turn.
One particular problem relating to vehicle handling relates to cornering of a two-wheel drive vehicle, such as a front wheel drive vehicle. When a driver applies the throttle of a front wheel drive vehicle, the longitudinal slip of the tires of the driven front axle increases and, due to the properties of pneumatic tires, the lateral force capacity of the tire (that is, the amount of additional force in a lateral direction that can be supported by the tire) will be reduced. If the throttle is applied during cornering when the force on the tires is already at or near the maximum amount of force in a lateral direction that can be supported by the tire (that is, the lateral force capacity is approaching zero), the increased longitudinal slip of the tires may cause the driven front axle to saturate, which may cause the vehicle yaw rate to decrease and the vehicle will be subjected to understeer (meaning that the front end of the vehicle moves towards the outside of the turn instead of following the desired path of the turn). Similarly, a rear wheel driven vehicle may be subject to oversteer during cornering for the same reasons.
There exist several ways of controlling the vehicle in order to counteract an oversteer or an understeer condition. For example, a torque vectoring mechanism may be used to distribute a torque between a left and a right rear wheel and in this way counteract the understeer or oversteer condition. More specifically, if the vehicle is subject to understeer in a turn, the torque vectoring mechanism may be controlled to increase the torque on the outer rear wheel. Conversely, if the vehicle is subject to oversteer in a turn, the torque vectoring mechanism may be controlled to increase the torque of the inner rear wheel.
There is a need for a method for controlling a torque vectoring mechanism, as well as a torque vectoring system, that provides improved performance.